Defence Secretary Michael Fallon visits HMS Vigilant, one of the UK's four nuclear warhead-carrying submarines at Royal Navy’s Faslane nuclear base on the Clyde.

Up to 12 can be mounted on each Trident missile, of which there are believed to be around 40 in service, with eight fitted to each vessel.

The Royal Navy has three nuclear-ready submarines in service with plans to replace the ageing fleet with a new generation of underwater deterrents.

GETTY

Defence Secretary Michael Fallon inside the Trident vessel

GETTY

Around 225 nuclear warheads are thought to make up Britain's submarine-based nuclear arsenal

GETTY

he Royal Navy has three nuclear-ready submarines in service

Last year former Labour defence secretary Lord Browne warned that UK nuclear weapons could "be rendered obsolete by hackers".

British Defence Secretary Michael Fallon has previously said the Government had a "moral responsibility" to protect the UK.

A Ministry of Defence (MoD) spokesman said: "The deterrent remains safe and secure.

"We take our responsibility to maintain a credible nuclear deterrent extremely seriously and continually assess the security of the whole deterrent programme and its operational effectiveness, including against threats from cyber."